This invention generally pertains to the field of urethane catalysts. More particularly, this invention relates to the use of amine molecules that incorporate a reactive hydrogen group as urethane catalysts.
The use of a catalyst in preparing polyurethanes by the reaction of a polyisocyanate, a polyol and perhaps additional ingredients is known. The catalyst is employed to promote at least two, and sometimes three major reactions that must proceed simultaneously and competitively at balanced rates during the process in order to provide polyurethanes with the desired physical characteristics. One reaction (usually referred to as the gel reaction) is a chain-extending isocyanate-hydroxyl reaction by which a hydroxyl-containing molecule is reacted with an isocyanate-containing molecule to form a urethane. This increases the viscosity of the mixture and provides a polyurethane-containing secondary nitrogen atom in the urethane groups. A second reaction is a cross-linking isocyanate urethane reaction by which an isocyanate-containing molecule reacts with a urethane group containing a secondary nitrogen atom. The third reaction that may be involved is an isocyanate-water reaction (usually referred to as the blow reaction) that by which an isocyanate-terminated molecule is extended and by which carbon dioxide is generated to blow or assist in the blowing of foam. This third reaction is not essential if an extraneous blowing agent, such as a halogenated, normally liquid hydrocarbon, carbon dioxide, etc., is employed, but is essential if all or even part of the gas required for foam generation is to be generated by this in situ reaction (e.g. in the preparation of “one-shot” flexible polyurethane foams).
The reactions must proceed simultaneously at optimum balanced rates relative to each other in order to obtain a good foam structure. If carbon dioxide evolution is too rapid in comparison with chain extension, the foam will collapse. If the chain extension is too rapid in comparison with carbon dioxide evolution, foam rise will be restricted, resulting in a high density foam with a high percentage of poorly defined cells. The foam will not be stable in the absence of adequate crosslinking.
Typically, the catalysts used for making polyurethanes are of two general types: tertiary amines (mono and poly) and organo-tin compounds. Organometallic tin catalysts predominately favor the gelling reaction, while amine catalysts exhibit a more varied range of blow/gel balance. Using tin catalysts in flexible foam formulations also increases the quantity of closed cells contributing to foam tightness. Tertiary amines can be effective as catalysts for both the blow and the gel reactions and are often used in combination with the organic tin catalysts.
Amine catalysts which strongly promote the water-isocyanate (blowing) reaction include tertiary amine structures based on the diethylenetriamine skeleton, in particular pentamethyldiethylenetriamine, and the β-(N,N-dimethylamino)alkyl ethers, in particular bis(N,N-dimethylaminoethyl)ether (described in U.S. Pat. No. 3,330,782). Most tertiary amines used for the catalysis of polyurethane foam forming reactions such as those described above are of the fugitive type. Fugitive amines are so designated because they are not bound to the urethane polymer matrix and, therefore, can leave the matrix under certain conditions. This fugitivity results in the emission of fumes from hot foam in both molded and slabstock foam processes, Air-borne, amine vapors can be an industrial hygiene problem in foam production plants. A particular effect of the amine vapor is glaucopsia, also known as blue-haze or halovision. It is a temporary disturbance of the clarity of vision. Fugitive amines can also cause problems, such as the fogging of automotive windshields, when they are used in the preparation of fully fabricated interior automotive parts. Many prior art fugitive amines also impart an unacceptably strong amine odor to the polyurethane foam. Because of these issues, there is increasing demand in the industry for low fugitivity, low odor catalysts.
Many approaches have been taken to define amine catalysts with reduced fugitivity. Amine catalysts that contain active hydrogen functionality (e.g. —OH, —NH2, and —NHR) often have limited volatility and low odor when compared to related structures that lack this functionality. Furthermore, catalysts that contain active hydrogen functionality chemically bond into the urethane during the reaction and are not released from the finished product. Catalyst structures that embody this concept are typically of low to moderate activity and promote both the blowing (water-isocyanate) and the gelling (polyol-isocyanate) reactions to varying extents.
Low odor, reactive catalyst structurally related to bis(N,N-dimethylaminoethyl)ether are described in U.S. Pat. Nos. 4,338,408 and 4,433,170. JEFFCAT® ZF-10 catalyst, 2-[N-(dimethylaminoethoxyethyl)-N-methylamino]ethanol, is an effective blowing catalyst, albeit less effective than bis(N,N-dimethylaminoethyl)ether.
Lastly, in many cases blends of catalysts containing different tertiary amine groups must be utilized in order to achieve the desired balance between gelling and flowing of foams. If a foam is out of balance, the foam will not be stable and will collapse.
It would be a substantial advance in the art if a new class of amine catalysts were discovered which overcome any of the just enumerated disadvantages of the prior art.